Method of preventing corrosion in pipe lines



April E.,L. HOFFMAN 2,195,989

' IETHOD OF PREVENTING CORROSION IN PIPE LINES Filed sptrb', 1937 TOVACUUM SOLVENT mniafApr. z, 1940 V'PATENT omes METHOD OF PREVENTINGCORROSION IN 7 PIPE LINES Edward L. Hoil'man, New York, N. Y., assignorto Socony-Vacuum Oil Company, Incorporated,

New York, N. Y., a corporation of New York Application Septembeiil, 1937Serial No. 182,303

5 Claims.

Pipe lines used for the transportation of gasoline and similar lightpetroleum fractions have been found to suffer from corrosion which isparticularly severe along the bottom portion of their internal surfaces,resulting in the formation of a 5 film of iron oxide which is dislodgedat frequent intervals and carried away in the flowing stream of oil. Notonly does this constant formation and dislodging of rustcorrode the pipeat a highly m accelerated rate, but the rust so carried away must beremoved, at considerable expense, from the product in which it issuspended, This corrosion of the interior of the pipe is not spreadevenly over the surface thereof but appears mainly as a channeling alongthe bottom of the pipe, requiring retirement of the pipe'from servicelong before the remainder of the pipe walls ,have deteriorated to anysubstantial degree.

. It is an object of this invention to provide a method for preventingthis specific form of corrosion in pipe lines carrying light petroleumfractions, and to provide a means of avoiding the deterioration ofproduct caused by the suspension therein of products of corrosionremoved from the pipe walls. A further object is to provide apparatusforcarrying out such a method.

This invention is based upon the discovery that corrosion of this type,with its formation and subsequent carryover 'of rust and the like, maybe prevented entirely by a method involving careful control of the watercontent of the petroleum fractions, particularly the gasoline, to bepumped through the pipe line, in proportion to the'temperatures to beencountered while the petroleum fraction remains in the pipe. In thefollowing discussion, gasoline is taken as exemplary of such petroleumfractions.

Gasoline, even whenfree of physically admixed water which may bedetected visually, still has in 50 of about 70 F., will contain about0.0080% by weight of water. The same gasoline, when cooled to about 40F., will contain only about'0.0040% by weight of water, thus havingprecipitated in 'the'neighborhood ct -about one-quarter of one pound ofwater per 1000 gallons of gasoline. In

it some dissolved water. The amount of this water, up to the solubilityof water in gasoline exist- (oi. lee-4S pipe lines, where the dailyquantity of gasoline handled is in quantities of the nature of 300,000gallons and upwards of gasoline per day, although the net temperaturechange from storage to line condition is slight, there is a sufflcientprecipitation of water due to this condition to give an appreciablethough small separation of water. It has been discovered that this waterdoes not remain dispersed in the gasoline but appears to migrate alongthe bottom of the pipe in the form of beads, droplets, or small streams.Likewise, the gasoline, or any other petroleum product, isalways more orless saturated with oxygen, up to the limit of its solubility in theoil. It has been determined that the corrosion is caused by the combinedaction of moisture and oxygen, localized in those areas of the internalsurface of the pipe exposed to such separated water.

In accordance with this invention this corrosion is prevented, and theattendant formation of rust and its dispersion in the oil is likewise beobtained only by control of the water dissolved in the gasoline, orother oil, as distinguished from other water which might be associatedwith the oil, either as a separate phase, or as an emulsion. In short,the oil must not only be dry, that is, entirely free from admixed oremulsified water of the kind which can be removed by the commonprocesses used for such purposes, but it must additionally have asubstantial amount of its dissolved water removed. Any dehydratingprocess (using that term in the manner now common in the art), whichfinally draws water and oil separately from some point where they existside by side as two phases, must necessarily provide oil which, whilefree of discrete water,

is saturated with dissolved water, and obviously would be entirelyuseless for the practiseof this invention. Therefore, inthisspecification, and a in the claims, when the term dehydration is used,it is used in the strict sense, meaning the removal" of dissolved.water.

.To understand this'invention', reference'is made to the attacheddrawing, wherein pipe I contains oil to be treated, 2 andj3 are chamberscontaining a dehydrating'chemicalfiand '4fis an" outflow pipe fortreatedoil. Oil entering through pipe I is diverted through pipe 5 to flowthrough chamber 2 and be dehydrated therein, leaving by pipe 6 to enterpipe I for delivery to the transportation system. When the dehydratingchemical in chamber 2 has been suiflciently saturated with water, theoil is diverted to chamber 3 by pipe I, returning to pipe 4 through pipe8. The dehydrating chemical may be regenerated by means of heating undervacuum, and for this purpose the chamber is provided with internal steamcoils, and .23, to which steam is led through pipes l6 and I8 and fromwhich condensate is removed by pipes l1 and I9. Vapors from regenerationare disposed of through pipes 20 and 2| which lead to a barometriccondenser or other convenient vacuum device not shown. Each chamber isprovided with a bottom draw pipe, l4 and I5, through which settledwater, if present, may be withdrawn. Also, I and I5 are connected bypipes and 26 to the vacuum device, in order that if necessary, vacuummay be applied to either end of the chambers. Since many productspresented for transportation have higher boiling points, such askerosene, and others, such as dyed gasolines, leave dye on thedehydrating chemical which would be taken by the next batch of oil, itis preferable to wash the chemical bed with a solvent as a portion ofthe regeneration step. This solvent may be introduced bypipe 9 throughpipes ill or II, and removed by pipes l2 and I3. The solvent wouldpreferably be a white petroleum product of low boiling point, such asundyed gasoline. If the treated oil has been kerosene or heavier, thislight solvent will dissolve and displace it upon the chemical and willitself be volatilized readily in regeneration, leaving the regeneratedchemical oil-free as well as water-free. Steam lines 24 and 25 are usedfor a purpose hereinafter explained.

The dehydrating chemical may be of any type capable of selectivelyremoving dissolved moisture from oil and capable of convenientregeneration. Those most convenient to use are the adsorbent activatedsolids, such as activated alumina, silica gel, various activated solidfgels, charcoal, some clays, and the like. Of these the medium atpresent preferred is activated alumina.

The dehydration of the petroleum fraction is carried to that point atwhich no moisture will separate at the temperature to be encountered inthe pipe line transportation system. That is to say, the dissolvedmoisture content is reduced to a value less than the saturation valuefor the expected pipe line temperature.

The control of degree of dehydration may be accomplished in either oftwo convenient methods. Freshly saturated or regenerated chemical willremove a high proportion of the water dissolved in the gasoline, sayaround 70%, for example. Relatively spent chemical will remove muchless, say 15% to 10% for example, and the proportionate amount removeddecreases progressively as the relative age of the chemical, betweenregeneration, increases. Now, the proper amount of reduction, dependentupon the degree of saturation, the storage temperature of the oil, andthe temperature to be expected in the pipe line is between thesefigures, ranging usually around 20 to reduction. The degree ofdehydration of the total oil can be controlled by sending only a portionof it through a relatively fresh chemical, securing a high proportionaldehydration, thereon, and blending back.

For example, with acharge of chemical capable of eifecting a 60%reduction in dissolved water on the gasoline under specific conditions,and a desired reduction of only 30%, half of the gasoline could betreated and when blended with the untreated half, the desired conditionwould be obtained. A more convenient method, however, and in fact, theone which is'preferred, is

' to have several dehydrating chambers as shown,

the oil being passed in parallel streams through several and the streamsbeing divided among them to arrive at the desired result. For example,with three chambers, one capable of 75% reduction, one of 50% reduction,and one of 25% reduction, with 50% overall reduction desired. then equalstreams could pass through each chamber and the blended product be asdesired. At the same time, a separate chamber would be undergoingregeneration, and as the efllciency of the three in use decreased towardlimiting operation, the one most spent could be isolated forregeneration, and the regenerated chamber placed on stream.

The amount of water picked up by the chemical is of course dependentupon the nature of the chemical. For activated alumina, the alumina willadsorb about 10% of its weight of water before requiring regeneration.

Regeneration details will depend somewhat upon the particular chemicalused. In general for the solid adsorbents and gels" it may beaccomplished by heating with coils 22 and 23 together with evacuating,or by introducing steam, preferably superheated, through 24 and 25, withor without heating by 22 and 23. superheated steam, when used, isfollowed by introducing heated air through the same means, to completedrying of the chemical. As pointed out previously, the final watercontent of the oil is dependent upon the conditions to be met in thepipe line. Under normal conditions, in the case of gasoline, thecorrosion may be reduced substantially by reducing the water content ofthe gasoline to from about 0.0030 per cent by weight, to about 0.0060per cent by weight, the lower concentrations being used concurrentlywith lower temperatures ,of the ground through which the pipe line isoperated, and corrosion may be entirely prevented by reducing the watercontent of the gasoline to a value not substantially in excess of from0.0020 to 0.0040 by weight. I

A convenient method of determining whether or not the gasoline has beendehydrated to a proper degree, is to dehydrate it previous to its entryto the pipe line, to such a degree that it does not thereafter decreasein water content during its passage through the pipe line, as may bedetermined by examinations of samples taken at points further along inthe piping system or at the point of delivery at the end of the pipeline.

While certain numerical data have been given herein they have been setforth only by way of example, and the invention is not limited theretoor thereby, but subject only to those limitations expressed in theclaims.

I claim:

1. A method of controlling internal corrosion of pipes carrying lightpetroleum fractions which fractions are initially entirely free of waterother than dissolved water comprising passing parallel streams of oilcontaining dissolved water through a plurality of chambers eachcontaining a water adsorbent material of a differing degree 01 activity,,removing dissolved water from said oil during the passage through saidchambers,

, blending said streams to secure a total product of a desired degree ofpartial dehydration, and passing said total product through the pipes.

2. A method of preventing internal corrosion of pipes carrying lightpetroleum fractions which fractions are initially entirely free oi!water other, than dissolved water comprising reducing the dissolvedwater content of the oil, before introduction to the pipe; .at least tosuch an extent water comprising reducing the dissolved water content ofthe gasoline, before entry to the pipe, to a quantity not substantiallyin excess of from about 0.0030 to about 0.0060 percent by weight.

.4. A method of preventing internal corrosion of gasoline-carrying pipelines by oxidation reactions comprising reducing the entire watercontent of the gasoline, including free water content and dissolvedwater content of the gasoline, before entry to the pipe, to a quantitynot substantially in excessof from about 0.0020 to about 0.0040 percentby weight.

5. In the transportation of light petroleum rdistillates through a pipeline characterized by the fact that said pipe line tends, upon passageof normally refined distillate therethrough, to deteriorate excessivelywith resultant contamination of the distillate; the method of inhibitingdeterioration of said pipe line and contamination of said distillatewhich comprises effecting the removal of. water from said lightpetroleum distillate including the removal of a substantial

